meadow fox-tail, cook's-foot, and fiorin. They con- 

 tained a considerable proportion of gypsum. 



Vitriolic impregnations in soils where there is no 

 calcareous matter, as in a soil from Lincolnshire, to 

 which I referred in the Fourth Lecture, are injurious; 

 but it is probably in consequence of their supplying an 

 excess of ferruginous matter to the sap. Oxide of 

 iron in small quantities forms an useful part of soils; 

 and, as is evident from the details ia the Third Lec- 

 ture, it is found in the ashes of plants; and probably, 

 is hurtful only in its acid combinations. 



I have just mentioned certain peats, the ashes of 

 which afford gypsum; but it must not be inferred from 

 this that all peats agree with them. I have examined 

 various peat, ashes from Scotland, Ireland, Wales, and 

 the northern and western parts of England, which 

 contained no quantity that could be useful; and these 

 ashes abounded in siliceous, aluminous earths and 

 oxide of iron. 



Lord Charleviile found in some peat-ashes from 

 Ireland sulphate of potassa; i. e. the sulphuric acid 

 combined with potassa. 



Vitriolic matter is usually formed in peats; and if 

 the soil or substratum is calcareous, the ultimate re- 

 sult is the production of gypsum. In general, when a 

 recent peat-ash emits a strong smell resembling that 

 of rotten eggs when acted upon by vinegar, it will fur- 

 nish gypsum. 



Phosphate of lime is a combination of phosphoric 

 acid and lime, one proportion of each. It is a com- 

 pound insoluble in pure water, but soluble in water 



